Abstract
Bovine anaplasmosis is a hemoparasitic disease that causes considerable economic loss to the dairy and beef industries. Cattle immunized with the Anaplasma marginale MSP1 outer membrane protein complex presents a protective humoral immune response; however, its efficacy is variable. Immunodominant epitopes seem to be a key-limiting factor for the adaptive immunity. We have successfully demonstrated that critical motifs of the MSP1a functional epitope are essential for antibody recognition of infected animal sera, but its protective immunity is yet to be tested. We have evaluated two synthetic vaccine formulations against A. marginale, using epitope-based approach in mice. Mice infection with bovine anaplasmosis was demonstrated by qPCR analysis of erythrocytes after 15-day exposure. A proof-of-concept was obtained in this murine model, in which peptides conjugated to bovine serum albumin were used for immunization in three 15-day intervals by intraperitoneal injections before challenging with live bacteria. Blood samples were analyzed for the presence of specific IgG2a and IgG1 antibodies, as well as for the rickettsemia analysis. A panel containing the cytokines’ transcriptional profile for innate and adaptive immune responses was carried out through qPCR. Immunized BALB/c mice challenged with A. marginale presented stable body weight, reduced number of infected erythrocytes, and no mortality; and among control groups mortality rates ranged from 15% to 29%. Additionally, vaccines have significantly induced higher IgG2a than IgG1 response, followed by increased expression of pro-inflammatory cytokines. This is a successful demonstration of epitope-based vaccines, and protection against anaplasmosis may be associated with elicitation of effector functions of humoral and cellular immune responses in murine model.
Highlights
Bovine Anaplasmosis manifested as a severe hemolytic disease is caused by an obligate intraerythrocytic bacterium, the Anaplasma marginale, endemic in tropical and subtropical regions, which can be transmitted biologically by ticks and mechanically by bloodcontaminated fomites or biting flies [1]
A. marginale Establishes Infection in Mice To evaluate the capacity of A. marginale infect mice, rickettsia inoculation was performed in 10 animals
We have successfully infected BALB/c mice with A. marginale, similar to what have been described for Human granulocytic anaplasmosis [26], and this mouse model of anaplasmosis proved to be a valuable tool to evaluate novel immunogens prior to bovine challenges
Summary
Bovine Anaplasmosis manifested as a severe hemolytic disease is caused by an obligate intraerythrocytic bacterium, the Anaplasma marginale, endemic in tropical and subtropical regions, which can be transmitted biologically by ticks and mechanically by bloodcontaminated fomites or biting flies [1]. It results in considerable economic loss mainly due to the low weight gain, reduction in milk production, abortion, treatment costs, and mortality [2]. Immunity against A. marginale is associated with these proteins, which are exposed in the rickettsia surface, are accessible by the host immune system, and can be neutralized by antibodies against exposed epitopes [12,13]. Cattle immunized with A. marginale outer membrane proteins developed high antibody titers and presented significant rickettsemia reduction if challenging with the pathogen when compared to adjuvant-immunized controls [14]
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